Habitat use by juvenile fish in macroalgae and seagrass beds in a temperate South African seascape

Structurally complex habitats such as seagrass, mangroves and macroalgae are important as nurseries in estuaries and nearshore marine environments. While numerous studies have focussed on structurally complex vegetated habitats in estuaries, fewer studies have focussed on vegetated nursery habitats (particularly macroalgae) in nearshore areas and their importance. In this study, stereo remote underwater video systems (sRUV) were used to examine the nature of shallow water vegetated habitat ( Zostera capensis and Plocamium corallorhiz a) usage by juvenile fish in the Algoa Bay shallow water seascape (Swartkops Estuary and nearshore). The two macrophytes habitats are different in structural complexity, with P. corallorhiza having more structural complexity indices higher than Z. capensis . Plocamium corallorhiz a had a higher juvenile total abundance, dominated by young-of-the year sparids. Although total juvenile abundance was lower in Z. capensis seagrass, the abundance of the estuarine-dependent sparid Rhabdosargus holubi (all young-of-the-year recruits) was higher in Z. capensis . Plocamium corallorhiz a had a higher species richness compared to Z. capensis . Differences in species composition (abundance and richness) may be associated with high habitat heterogeneity in macroalgal sampling sites. Exhibited behaviours by juveniles in both habitats were dominated by slow meandering and feeding, behaviours associated with a high level of habitat use. In terms of fish community composition, both macrophyte habitats grouped broadly together but were statistically distinct from fish communities in unstructured sand. • Zostera capensis seagrass and Plocamium corallorhiza macroalga provide comparable habitat complexity. • Zostera capensis seagrass and Plocamium corallorhiza macroalga beds are dominated by young-of-the-year sparids. • Total juvenile fish abundance was higher in macroalgae than seagrass beds. • Both macrophyte types provide important nursery habitat with their nursery function not interchangeable.